The present invention relates to a semitransparent liquid crystal display device with high intensity and low power consumption.
With the widespread use of mobile terminals and other similar equipment, the reflective liquid crystal panel has been drawn attention. This type of panel reflecting outer light for display shows sufficient display performance in bright conditions like outdoors; however, its visibility remarkably decreases in dark conditions.
In order to overcome this problem, a semitransparent liquid crystal panel capable of being used both indoors and outdoors has been developed by applying the technique of the reflective liquid crystal panel. In such a semitransparent liquid crystal panel, when a backlight is employed, each transparent portion in the form of a square is arranged at the center of a pixel in reflective layers which have a projections and depressions structure. In order to simplify manufacturing requirements, the projections and depressions structure is identical in all pixels (Refer to Japanese Laid-open Patent Application No. 10-319422).
However, in the case where such a large transparent portion is provided at the center of each pixel in the reflective layers, as in the above prior art case, the large total area of the transparent portions are irrelevant to reflection; intensity is insufficient when the panel is used as reflective type. As another problem, since the intensity in the reflective type is determined by the area of the transparent portions, providing transparent portions without regard to the projections and depressions structure makes reflectivity during reflection and permeability during permeation incompatible.
If the color filter layer has the same degree of thickness during permeation and during reflection, there is a problem that light has different degrees of absorption between during reflection and during permeation, thereby making color phases differ between during reflection and during permeation. The reason for this is considered that during reflection, light goes through the color filter layer and then returns through it, substantially making the color filter layer twice as thick as it is during permeation. As a result, for example, when a color filter for reflection with high permeability is used by giving reflectivity priority, there is a problem that the color is lightened during permeation
Further the pixels having the same projections and depressions structure also have the same capacity within the screen. Therefore, when the screen is larger, there is a problem that a decrease in gate voltage due to the line resistance of the gate and the source makes the punch-through voltage show different values within the screen, thereby causing flicker.
In order to solve the above-described problems, the inventors of the present invention have achieved a semitransparent liquid crystal display device with backlighting comprising semitransparent reflective layers having a projections and depressions structure as follows.
A first aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein said transparent portions are so formed as to include nearly flat regions of said projections and depressions structure.
The nearly flat regions (regions of extremely small angles of inclination) in the projections and depressions structure do not contribute to an increase in panel reflectivity, and what is worse, deteriorate display performance because they cause specular reflection. Therefore, by so forming transparent portions as to include the nearly flat regions of the projections and depressions structure, the specular reflection can be prevented. In addition, the presence of the transparent portions can improve the permeability of light emitted from the backlight. The specific effects of the transparent portions will be described in the effects for a second aspect of the invention.
A second aspect of the invention is characterized in the first aspect of the invention, wherein the projections and depressions structure in the nearly flat regions has the angle of inclination of not less than 0 degree nor more than 2 degrees.
The reflection performance of the semitransparent layers having the projections and depressions structure is determined by the angle of inclination of the projections and depressions structure in the reflective portions. In order to efficiently gather ambient light in the viewer""s direction, it is necessary to arrange the angle of inclination of 2 to 10 degrees degrees in a specific distribution. Asperities having the angle of inclination of less than 2 degrees are likely to cause specular reflection and are not effective in light-gathering. The specular reflection causes degradation reverse, which remarkably lowers visibility. Thus, regions having the angle of inclination less than 2 degrees do not contribute to an increase in the panel reflectivity, and what is worse, may deteriorate the display performance due to the specular reflection. For this reason, in prior art devices, the reflective layers have been so arranged as not to create regions with small angles of inclination. However, the inventors of the present inventions have found that in a semitransparent display with backlighting, devoting the regions with small angles of inclination to transparent portions not only prevents the occurrence of specular reflection but also improves the panel reflectivity.
The specific effects of the present invention will be described as follows in comparison with a prior art device.
FIGS. 1 and 2 respectively show the top view and a cross sectional view of the array substrate of the liquid crystal panel in the prior art semitransparent liquid crystal display device. In the prior art device, the projections and depressions structure 204 is made from a resist in such a manner that as small flat regions as possible are created so as to prevent the reflective layers 202 from having small angles of inclination. However, no manner how the structure 204 is arranged, the peaks of the projective portions must be nearly flat, so that the reflective layers 202 are formed even in the nearly flat regions. On the other hand, since a large transparent portion 205 not provided with the reflective layers 202 is arranged at the center of a pixel so as to realize the semitransparent type, the projections and depressions structure 204 in the transparent portion 205 does not contribute to an increase in the reflectivity at all.
FIG. 3(a) shows an example of light trails on the reflective layers of the prior art semitransparent liquid crystal display panel. Light 210 reflected on an inclined surface in the projections and depressions structure 204 contributes to an increase in intensity, while light 211 regularly reflected near the peak of a projective portion is one cause of degradation reverse. Furthermore, the inclined surfaces of the projective portions in the transparent portions 213 are provided with transparent electrodes 214 only so that transparent light 215 can be generated without regard to the projections and depressions structure 204. Therefore, the inclined surfaces of the projective portions in the transparent portion 213 do not contribute to an increase in the panel reflectivity at all.
In contrast, the semitransparent liquid crystal display device of the present invention devotes the nearly flat regions of the projections and depressions structure in the reflective layers to transparent portions, which prevents a decrease in panel reflectivity and improves intensity during permeation. Thus devoting the regions not contributing to an increase in the panel reflectivity to transparent portions, both the reflectivity and the permeability can be improved.
FIG. 3(b) shows an example of light trails on the reflective layers of a semitransparent liquid crystal display panel of the present invention. Each transparent portion 301 having a transparent electrode 300 is formed near the peak of a projective portion. Light 302 reflected on an inclined surface which contributes to an increase in reflection performance is generated on the entire surface of the pixel, thereby improving the panel reflectivity. Furthermore, devoting the regions near the peaks of the projective portions which would cause degradation reverse in the prior art structure to the transparent portions 301 reduces the occurrence of gradation reverse and also secures the permeability of the backlight. These effects result from the fact that the panel permeability is determined by the total area of the transparent portions 301.
A third aspect of the invention is characterized in the first aspect of the invention, wherein the projections and depressions structure in the nearly flat regions has the angle of inclination of not less than 0 degree nor more than 4 degrees.
When the regions having the angle of inclination not more than 4 degrees are defined as nearly flat regions, the reflectivity decreases near the regular reflection direction, while the reflectivity in the visibility direction away from the regular reflection direction remains the same, thereby further improving the permeability.
A fourth aspect of the invention is characterized in the first aspect of the invention, wherein at least some of the transparent portions do not have transparent electrodes.
When the transparent portions are small in area, even if they do not have transparent electrodes, the electric field response of the liquid crystal on the transparent portions becomes possible in the electric field between the ambient reflective layers and the counter layers. Consequently the same effects as above can be obtained.
A fifth aspect of the invention is characterized in the first aspect of the invention, wherein the transparent portions have transparent electrodes.
As stated above, this is because if the transparent portions have a small area, transparent electrodes are dispensable; however, if they have a large area, it is preferable that they have transparent electrodes.
A sixth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein said transparent portions are so formed as to at least partly include projective portions of said projections and depressions structure.
Since the projective portions include nearly flat regions, areas including the nearly flat regions can be devoted to transparent portions so as to obtain the same effects as those of the first aspect of the invention.
A seventh aspect of the invention is characterized in the sixth aspect of the invention, wherein the transparent portions include peaks of the projective portions and are formed symmetric with respect to the peaks.
When the transparent portions are formed in the areas including at least the peaks of the projective portions of the projections and depressions structure, the peaks of the projective portions are the nearly flat regions of the projections and depressions structure, which can prevent a decrease in panel reflectivity and improve intensity during permeation. In other words, the devotion of the areas not contributing to an increase in the panel reflectivity like the peaks in the projective portions to the transparent portions can improve both the reflectivity and the permeability.
A eighth aspect of the invention is characterized in the sixth aspect of the invention, wherein the transparent portions include peaks of the projective portions and are formed asymmetric with respect to the peaks.
A ninth aspect of the invention is characterized in the sixth aspect of the invention, wherein the transparent portions are formed on half surfaces of the projective portions.
When the transparent portions are provided on the half surfaces of the projective portions to be more specific, when the transparent portions are mainly provided on the half surfaces of the projective portions on the viewer""s side and the reflective layers are provided on the other half surfaces, even if outer light is reflected by the viewer""s body and goes into the panel from the viewer""s side, the light is discharged through a transparent portion out to the rear side. As a result, mirroring is decreased and visibility is improved.
A tenth aspect of the invention is characterized in the sixth aspect of the invention, wherein a cross section of the projective portions has an asymmetrical figure comprising a plurality of inclined surfaces, and the transparent portions are formed on steeply-inclined surfaces of the asymmetrical figure.
When the steeply-inclined surfaces are arranged on the viewer""s side, light from the backlight goes diagonally from the transparent portions on the projective portions, which improves the intensity during permeation. Since approximately the entire surface becomes the reflective layers when seen from above, there is another effect of improving the reflectivity.
An eleventh aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein a cross section of the projective portions of the projections and depressions structure is trapezoids, and the transparent portions are so formed as to at least partly include the top surfaces of the trapezoids.
Since the top surfaces of the trapezoids are nearly flat, the transparent portions can be so formed as to partly include the nearly flat top surfaces, thereby obtaining the same effects as above.
A twelfth aspect of the invention is characterized in the eleventh aspect of the invention, wherein the top surfaces of the projective portions are polygonal.
By making the top surfaces of the projective portions polygonal, the bearing angle of the inclined surfaces can be set freely, facilitating the adjustment of the visual angle.
A thirteenth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein the transparent portions are so formed as to include at least the bottoms of depressive portions of the projections and depressions structure.
A fourteenth aspect of the invention is characterized in the thirteenth aspect of the invention, wherein the depressive portions of the projections and depressions structure have bottoms, and the bottoms are nearly flat.
If the transparent portions are so formed as to include at least the nearly flat regions of the depressive portions, the nearly flat regions of the depressive portions do not contribute to the panel reflectivity, which makes it possible to improve both the panel reflectivity and the permeability. This will be described more specifically with reference to FIG. 4. FIG. 4 shows the light trails on the reflective layers of another semitransparent liquid crystal panel of the present invention. Regions 401 between projective portions 400 can be made nearly flat and be used as transparent portions so as to improve both reflectivity and permeability.
A fifteenth aspect of the invention is characterized in the thirteenth aspect of the invention, wherein the reflective portions are formed asymmetric with respect to the peaks of the projective portions.
A sixteenth aspect of the invention is characterized in the fifteenth aspect of the invention, wherein the reflective portions are formed on half surfaces of the projective portions.
As shown in FIGS. 5(a) and 5(b), when the reflective portions are provided asymmetric with respect to the peaks of the projective portions, the outer light can be gathered effectively in the viewer""s direction by the same principle as stated above. When the reflective portions 410 are provided more in the side opposite to the viewer""s side in the projective portions as shown in FIG. 5(a), the outer light coming from the side opposite to the viewer""s side can be collectively gathered. On the other hand, when the reflective portions 410 are provided more in the viewer""s side as shown in FIG. 5(b), the outer light reflected by the viewer""s body or coming from the back of the viewer can be collectively gathered. When the patterns of FIGS. 5(a) and 5(b) are mixed in an appropriate ratio, their respective light-gathering properties can be averaged in accordance with the mixture ratio, thereby adjusting the light-gathering properties more effectively.
A seventeenth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein the transparent portions are formed at least in regions including the peaks of the projective portions and in regions including the bottoms of the depressive portions.
In this structure, both the reflectivity and the permeability can be further improved.
A eighteenth aspect of the invention is characterized in the seventeenth aspect of the invention, wherein both the peaks of the projective portions and the regions including the bottoms of the depressive portions are nearly flat.
A nineteenth aspect of the invention is characterized in the eighth aspect of the invention, wherein the transparent portions are formed separately from each other.
A twentieth aspect of the invention is characterized in the eleventh aspect of the invention, wherein the transparent portions are formed separately from each other.
A twenty-first aspect of the invention is characterized in the nineteenth aspect of the invention, wherein the transparent portions are arranged at random.
A twenty-second aspect of the invention is characterized in the twentieth aspect of the invention, wherein the transparent portions are arranged at random.
Thus arranging the transparent portions at random realizes a panel without having diffraction, coloring, or inconsistencies in intensity.
A twenty-third aspect of the invention is characterized in the thirteenth aspect of the invention, wherein the transparent portions are partly connected with each other.
A twenty-fourth aspect of the invention is characterized in the seventeenth aspect of the invention, wherein the transparent portions are partly connected with each other.
A twenty-fifth aspect of the invention is characterized in the thirteenth aspect of the invention, wherein the reflective portions are partly connected with each other.
A twenty-sixth aspect of the invention is characterized in the seventeenth aspect of the invention, wherein the reflective portions are partly connected with each other.
When the reflective portions are made from conductive material, connecting the reflective portions partly with each other facilitates the electric connection in the contact hole.
A twenty-seventh aspect of the invention is characterized in the thirteenth aspect of the invention, wherein a color filter layer is formed on the projections and depressions structure, and the color filter layer has a thickness of d1 on the projective portions and a thickness of d2 on the depressive portions, the thickness d2 being greater than the thickness d1.
A twenty-eighth aspect of the invention is characterized in the seventeenth aspect of the invention, wherein a color filter layer is formed on the projections and depressions structure, and the color filter layer has a thickness of d1 on the projective portions and a thickness of d2 on the depressive portions, the thickness d2 being greater than the thickness d1.
Light entering as outer light and reflected by the reflective layers permeates through the portions of the color filter layer that have a thickness of d1. The outer light permeates through the color filter layer before reaching the reflective layers, and again permeates through the color filter layer after being reflected by the reflective layers in other words, the outer light permeates through the color filter layer of the thickness d1 twice. On the other hand, transparent light emitted from the backlight through the depressive portions permeates through the color filter layer of the thickness d2 only once. Consequently, even if a color filer layer for reflection with high permeability is used, the transparent light from the backlight passes through the portions of the color filter layer that have a larger degree of thickness, so that enough color reproducibility can be obtained in the case of transparent light.
A twenty-ninth aspect of the invention is characterized in the twenty-seventh aspect of the invention, wherein the thickness d2 is approximately two times larger than the thickness d1.
A thirtieth aspect of the invention is characterized in the twenty-eighth aspect of the invention, wherein the thickness d2 is approximately two times larger than the thickness d1.
In the above structure, the transparent light from the backlight and the outer light have an equal distance to pass through the color filter layer, so that the obtained color reproducibility is approximately equal during permeation and during reflection.
A thirty-first aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure, the semitransparent layers partly overlaying a gate line on a substrate, wherein capacitance in an overlaid area of the semitransparent layers with the gate line decreases with increasing distance from a gate writing side of a liquid crystal panel.
A thirty-second aspect of the invention is characterized in the thirty-first aspect of the invention, wherein an average degree of thickness of said overlaid area increases with increasing distance from the gate writing side of said liquid crystal panel.
A thirty-third aspect of the invention is characterized in the thirty-second aspect of the invention, wherein an area ratio of the projective portions to the depressive portions in the overlaid area increases with increasing distance from the gate line side of the liquid crystal panel.
A thirty-fourth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure, the semitransparent layers partly overlaying a source line on a substrate, wherein capacitance in an overlaid area of the semitransparent layers and the source line decreases with increasing distance from a gate writing side of a liquid crystal panel.
A thirty-fifth aspect of the invention is characterized in the thirty-fourth aspect of the invention, wherein an average degree of thickness of the overlaid area increases with increasing distance from the gate writing side of the liquid crystal panel.
A thirty-sixth aspect of the invention is characterized in the twenty-fifth aspect of the invention, wherein an area ratio of the projective portions to the depressive portions in the overlaid area increases with increasing distance from the gate line side of the liquid crystal panel.
A thirty-seventh aspect of the invention is characterized in the thirty-first aspect of the invention, wherein the capacitance changes continuously.
A thirty-eighth aspect of the invention is characterized in the thirty-fourth aspect of the invention, wherein the capacitance changes continuously.
The effects of the thirty-first to the thirty-eighth aspects of the invention will be described as follows.
During the panel is being operated, the gate voltage decreases due to the line resistance of the gate as it gets far from the writing side. As a result, when the pixels have a uniform capacity within the screen, flicker occurs after writing. The counter potential Vcom necessary to eliminate the flicker differs within the screen. Difference xcex94Vcom in counter potential at each position within the screen, as compared with the counter potential Vcom on the line side is expressed in Formula (1) below.
xcex94Vcom=[(Cst+Cgd+Csd)/Clc]xc3x97xcex94Vgxe2x80x83xe2x80x83(1)
Cst: storage capacity
Cgd: gate-drain capacity
Csd: source-drain capacity
Clc: liquid crystal capacity
xcex94Vg: difference in gate voltage at each position within the screen, as compared with the initial value of the gate voltage on the line side
In order to reduce flicker, it is necessary to maintain xcex94Vcom below a fixed value, even if xcex94Vg continuously increases with increasing distance from the writing side. Therefore, it is necessary to reduce all or either one of Cst, Cgd, and Csd in accordance with an increase in xcex94Vg.
The parasitic capacity due to the projections and depressions structure formed in the overlaid area of the gate line with the reflective layers is included in Cst in terms of an equivalent circuit. Consequently, the parasitic capacity due to the projections and depressions structure formed in the overlaid area of the gate line with the reflective layers with increasing distance from the writing side can be decreased, so as to obtain the effect of reducing flicker. The degree of a decrease in potential due to the resistance of the gate line continuously increases in accordance with the distance from the writing side, provided that the lines have a uniform width. As a result, continuously changing the parasitic capacity can reduce flicker further effectively.
The parasitic capacity can be changed by the average degree of thickness of the projections and depressions structure formed in the overlaid area of the gate line with the reflective layers. The average degree of thickness is defined by the value obtained by dividing the volume of the overlaid area by the bottom space of the overlaid area. Alternatively, the parasitic capacity can be changed by varying the area ratio of the projective portions to the depressive portions. This can be done because the average degree of thickness increases when the projective portions are larger in area than the depressive portions, and decreases when the depressive portions are larger in area.
Generally, when nearly flat reflective layers are used, the space of the overlaid area is changed, and the degree of thickness is fixed so as to continuously change the value of the parasitic capacity for each pixel. This is because it is difficult to change the degree of the thickness of the layers which is determined by how it is deposited from pixel to pixel. However, by using the layers having the projections and depressions structure, the value of the parasitic capacity is easily changed by the ratio of the projective portions to the depressive portions, even if the resist is deposited with a uniform degree of thickness. On the other hand, in a semitransparent panel with the projections and depressions structure, if the parasitic capacity is changed by the space of the overlaid area, regions without the projections and depressions structure are expanded, which decreases intensity and causes its variations within the screen, thereby degrading the display quality. However, by changing the parasitic capacity by varying the ratio of the projective portions to the depressive portions, the projections and depressions structure can be formed on the entire surface, eliminating the occurrence of problems such as an intensity decrease. Consequently, in a semitransparent panel comprising semitransparent layers having the projections and the depressions structure, the occurrence of flicker can be effectively prevented by changing the ratio of the projective portions to the depressive portions that is, average degree of thickness.
The parasitic capacity of the overlaid area of the reflective layers with the source line is included in Csd in Formula (1). Therefore, in the same principle as above, the occurrence of flicker can be reduced by decreasing the parasitic capacity due to the projections and depressions structure formed in the overlaid area of the source line with the reflective layers with increasing distance from the writing side. In this case, too, it is effective to change the parasitic capacity by the average degree of thickness of the projections and depressions structure.
A thirty-ninth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein the transparent portions are so formed as to include at least the peaks of projective portions of the projections and depressions structure, and micro lenses are arranged under the projective portions.
In this structure, light from the backlight is gathered by micro lenses and emitted through the transparent portions arranged at the peaks of the projective portions, thereby achieving high intensity during permeation
A fortieth aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein pixels comprise the transparent portions of different area ratios.
In this liquid crystal display device, variations in intensity occur in accordance with the distance from the backlight. The intensity of the panel is likely to increase as it is closer to the backlight. Therefore, intensity within the screen can be uniformed by changing the area ratio of the transparent portions to the pixels according to the position within the screen. To be more specific, the area ratio of the transparent portions can be made smaller as they are closer to the backlight.
A forty-first aspect of the invention is characterized in the fortieth aspect of the invention, wherein the transparent portions have a range of area ratio where panel reflectivity is approximately constant.
When the transparent portions are arranged in the nearly flat regions in the projections and depressions structure, the regions do not contribute to an increase in panel reflectivity, so that the panel reflectivity becomes approximately constant without regard to the area ratio of the transparent portions. Therefore, the intensity within the panel screen can be uniformed both during permeation and during reflection.
A forty-second aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein the transparent portions are formed in regions where the projections and depressions structure has the angle of inclination of not less than 10 degrees.
A forty-third aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein the transparent portions are formed in regions where the projections and depressions structure has the angle of inclination of not less than 10 degrees and in regions where the projections and depressions structure has the angle of inclination of not more than 2 degrees.
The distribution of the angles of inclination of the projections and depressions structure has a strong correlation with the reflection properties of the panel. For example, when light enters with the angle of 30 degrees and the reflected light is gathered in the polar angle of 0 to 25 degrees, the angle of inclination involved with light-gathering is in the range of about 2 to 10 degrees. The light reflected in the nearly flat regions of less than 2 degrees becomes light of regular reflection, which causes display defect. On the other hand, the light reflected in regions having a large angle of inclination of not less than 10 degrees is either reflected to the side opposite to the direction of visibility or enclosed inside the panel without being involved with light-gathering. Consequently, as stated above, even if the regions with the angle of inclination of not less than 10 degrees are included in the transparent portions in addition to the nearly flat regions, the reflection properties within the visible range remain the same. Furthermore, the intensity during permeation is improved by the expansion of the area of the transparent portions.